A conventional navigation system used in a vehicle is equipped with a location function that detects a current position of the vehicle by using a position detector and displays the position detected on a screen of a display unit together with a map. Further, such navigation system is also equipped with a route guidance function that provides route guidance by searching a recommended route to a user-specified destination and by notifying the recommended route by voice or by graphic. The current position of the vehicle is detected and determined based on information regarding an absolute position from GPS signals, detection signals from a vehicle speed sensor, an angular velocity sensor, and by estimating a travel locus of the vehicle and by matching such locus with road map data.
A navigation apparatus of Japanese patent No. 4,645,516 (JP '516) discloses a special lane on a road, which is designated either as a high occupancy vehicle (HOV) lane or a carpool lane. A vehicle is allowed to travel in the HOV lane only when the vehicle is occupied by a predetermined number of occupants or more, thereby encouraging a shared use of vehicles and reducing the total number of vehicles on the road. If the vehicle is not occupied by the predetermined number of occupants when traveling in the HOV lane, the driver of the vehicle is fined. The HOV lane is thus less congested than other lanes, allowing compliant vehicles to travel faster for reaching the destination.
Further, though the HOV lane may be structured as a different road from other roads, the HOV lane may sometimes be an adjacent lane of a normal lane of the same road, with two parallel-running normal and HOV lanes simply divided by a division line (i.e., a lane mark) or by a guardrail. Even when the HOV lane is divided by the lane mark, entering into the HOV lane or exiting from the HOV lane from/to the normal lane may only be allowed at a predetermined road section (e.g., an access permit section). The HOV lane may be distinguished from the normal lane of the road by, for example, a diamond shape paint on the road (i.e., a road mark) or a road sign standing beside the road.
When the route guidance is provided by the vehicle navigation system, the user (i.e., a driver) may set an HOV option of the navigation system for using the HOV lane, if the number of occupants satisfies an HOV lane use condition. In such manner, the navigation system automatically takes into consideration (i.e., into calculation of the guidance route) the HOV lane whenever the HOV lane is available as the route guidance, for providing an appropriate guidance for smooth entrance into the HOV lane and for smooth exit from the HOV lane as required.
The vehicle may, however, travel in the normal lane for some reason, even when the navigation system is capable of providing an HOV lane considered route guidance. In such a situation, the following problem may be experienced.
FIGS. 8A and 8B illustrate a situation where a vehicle A and a vehicle A′ are respectively traveling along a highway (i.e., northbound highway H1) towards a junction to enter another highway (i.e. westbound highway H2). The northbound highway H1 has four lanes with an HOV lane L on the left-most side and the other three lanes L0 serving as normal lanes. The westbound highway H2 also has four lanes with an HOV lane L on the left-most side and the other three lanes L0 serving as normal lanes. When the vehicles A and A′ receive guidance for transitioning from the northbound traffic (i.e., an arrow “a”) of H1 to the westbound traffic (i.e., an arrow “b”) of H2, the following problem may occur.
With reference to FIG. 8A, if the vehicle A is actually traveling in the HOV lane L, with the route guidance instructing the travel of the HOV lane L, the vehicle A can branch from the left-most HOV lane L of H1 to the left-most HOV lane L of H2 through an HOV lane dedicated ramp W1 as indicated by a thick broken arrow line. The route guidance of such transit may sound like “Keep left onto HWY-2” at a preset point before the ramp W1.
However, with reference to FIG. 8B, if the vehicle A′ is traveling in one of the normal lanes L0, such as the second lane from the right, the vehicle A′ cannot change lanes from the normal lane L0 to the HOV lane L at a guidance provision timing when the route guidance of “Keep left onto HWY-2” is provided at a preset point before the ramp W1. Thus, the driver may have to pass the junction and then turn around to try to enter H2.
When the vehicle A′ is traveling in the normal lane L1, the vehicle A′ should receive the route guidance, which guides the vehicle A′ to enter the right-most lane L0 of H1 to branch off to the right-most lane L0 of H2 through a normal lane ramp W2, as shown by a thick broken arrow line in FIG. 8B. The route guidance in such case should sound like “Keep right onto HWY-2” at a preset point before the ramp W2.
Therefore, the navigation system may preferably determine whether the vehicle is traveling in the HOV lane or in the other lane (i.e., the normal lane) for the purpose of providing an appropriate route guidance that uses, as a guidance route, a road having the HOV lane. However, the position detector of the current navigation system may not be able to detect each of the lanes on the road due to a relatively large amount of error of the detector.
Therefore, in JP '516, whether the vehicle is traveling in the HOV lane is detected by capturing a road sign or a road mark with the in-vehicle camera and by performing image recognition for the captured image. Accordingly, in addition to the normal position detector of the navigation system, the determination of the travel of the vehicle in the HOV lane may only be possible with a special device that captures an image and recognizes the captured image.